Wave guide stub



y 1952 J. F. ZALESKI 2,596,458

WAVE GUIDE STUB Filed April 23, 1949 2 SHEETS-SHEET l Zmnentor JOHN F.ZALESKI attorney May 13, 1952 J z s 2,596,458

WAVE GUIDE STUB Filed April 23, 1949 2 SHEETS SHEET 2 Gttorneg PatentedMay 13, 1952 WAVE GUIDE STUB John F. Zaleski, Queens Village, N. Y.,assignor to General Precision Laboratory Incorporated, a corporation ofNew York Application April 23, 1949, Serial No. 89,267

2 Claims. (01. 178-44) This invention relates to a tunable wave guidestub and particularly to an improved device for introducing variablereactance into microwave circuits.

Circuits for microwave energy employ transmission lines which areuniquely different from those used in lower frequency circuits, andwhich in general consist of hollow wave guides, coaxial transmissionlines or dielectric rods. Inductive and capacitive devices for use withsuch lines also bear little resemblance to those employed at lowerfrequencies.

One such device commonly used for continuous adjustments of impedancefrom a low positive reactance value through infinity to a low negativereactance value consists of a short length of rectangular hollow waveguide short-circuited at one end by a movable plunger and open at theother end for attachment to microwave guide in either series or shuntconnection. 7

This form of device is designed for use with rectangular hollow waveguide and when connected into a broad side of such a guide to form aseries arm its reactance is presented to the guide as series reactance,while if connected into a narrow side to form a shunt arm its reactanceis in shunt with that of the guide. While such a tunable stub has beenthe best variable reactance means heretofore available and has beenwidely used it suifers from the faults of mechanical complexity andcost. The slidable plug must be precisely made and should incorporatequarter-wave or half -wave trap slots to prevent escape of microwaveenergy around its edges. Likewise these devices have sliding contactswhich are disadvantageous.

The instant invention provides a tunable stub which substitutes for thesliding end plug an adjustable fin of thin sheet material projectingthrough a longitudinal slot into the interior of the guide. It thussubstitutes for the intricate and costly sliding plunger a simply madeand easily operated fin of sheet material, greatly simplifying thedesign and facilitating its employment.

The exact nature of the invention will be more readily understood fromthe following detailed description when considered with the attacheddrawing in which:

Figure 1 illustrates one form of the invention applied to a series stub.

Figure 2 illustrates a similar to a shunt stub.

Figure 3 is a side view of a modified form of the invention.

device as applied Figure 4 is a plan view of the modification of Figure3.

In Figure 1 a section of hollow rectangular wave guide II is closed atone end by a solid conductive plate I2 soldered or brazed to the guide.At the other end l3 the guide is fastened into an opening in a broadside of another section of guide l4 so that the first section is aseries arm of the second section. This second section I4 represents anywave guide or microwave equipment through which microwave energy mayfiow and which may require for any purpose a tunable wave guide stubattached as :a series arm.

The stub section II is provided with a slot l8 cut in the center line ofone of its broad faces and in which is variably positioned a fin iscom-- posed of metal or a good dielectric, the former being preferableas the effects produced thereby are somewhat more pronounced. The fin I9is hinged to the stub section I l by means of a hinge pin 2| whichpasses through one end of the fin and the cooperating arms ll and 42 ofa bracket 43 fastened to the stub section. This rotation of the finabout its pivot point 2| varies the depth of insertion of the fin in thestub section.

To facilitate this adjustment an adjusting screw 22 and compressionspring 23 cooperate with an extension 45 on the fin l9 in such fashionthat the fin may be moved in either direction without lost motion. Tothis end the screw 22 is in threaded engagement with a leg 44 of thebracket 43 and has its end bearing on the upper edge of the extension 46of the fin [9 while the spring 23 is positioned between the uppersurface of the stub section II and the under edge of the extension 46.Rotation of the adjusting screw in one direction thus causes the fin l9to be rotated in a counterclockwise direction against the force of thespring 23 and increases the depth of insertion of the fin I9 in the stubsection II. Rotation of the adjusting screw in the other direction,however, permits the spring 23 to rotate the fin Is in the oppositedirection and results in a reduced depth of penetration of the stub H bythe fin 19.

The fin may be shaped as illustrated, that is, constituting a segment ofa circle, or it may be of any other desired shape so long as the shapechosen is such that variation in depth of insertion produces a gradualchange in the area of the fin which is contained in the stub section II.

If desired the slot l8 may be provided with coamings in the form ofone-quarter wave or one-half wave traps to prevent radiation thereby asmore fully illustrated and described in the V copending applicationSerial No. 86,293, dated April 8, 1949, of John F. Zaleski, now PatentNo. 2,591,329 issued April 1, 1952.

Fig. 2 illustrates the closed-end guide stub ll of Fig. 1 attached as ashunt arm to a narrow side of another section of wave guide 11 which,like the guide M of Fig. 1, represents any wave guide or microwaveequipment through which rnicrowave energy may flow and which may resizeof rectangular hollow guide chosen are trans mitted through'the guidesection I4. With the fin Hiremoved entirely from the interior of theguide, the sign and amount of the reactance which the stub -H offers inseries with the guide M at the stub opening 13- depends entirely uponthe magnitude of its length L. This reactance has-avalue'ofinfinity whenL equals one-quarter wavelength in-the-guideor any odd integral multiplethereof, andis zero ifL is'one-half wavelength or any multiple of it.Between these values 'the reactance offe'red ranges through allinductive and capacitive values. For instance, when L is between and AM,where A is the wavelength in the guide, or in general between where N isany integer, thereactance is inductive and rangesf rom zero to infinity.For lengths between %/\g and. or in general from 75 H 2 'th'ereactanc'eis capacitiveand'ranges from in- 'finity to zero. I

It has beenffou'nd th t when a fin such asfin 7 E9 in Fig. 1 is insertedlongitudinally into a broad side of a hollow rectangular wave guide,micro- Waves passing through the guide are retarded, and the amount-ofretardation is representative of both the depth of insertion and thelength of the inserted portion of the fin. 'If the insertion guide stubsuch as stub II in Figs. 1 and 2, the electrical length of the stub isincreased as the fin is lowered into the guide, for theretardationproduced by the fin is equivalent to a phase lag and the effect iselectrically similar to the effect produced by increasing the physicallength L of the stub. This permits adjustment of the stub by means ofthe fin to have any value whatever of reactance. For instance, if thelength L is chosen to be and the fin is made large enough to be capableof producing at maximum insertion a retardation of at least 180, thenthe electrical length of the stub may be varied by means of the fin froma length of when the-fin is out of the guide to an electrical length of)\g when the fin is inserted'to its maximum permissible depth. As beforedescribed these lengths offer at the open mouth I3 of the stub allpossible values of reactance ranging from zero through all inductivevalues to infinity, then from infiity throughall capacitive-valuestozero. These values are interposed in series withthe guide section I 4in Fig. 1. r

In Fig. 2 exactly the same description applies except that the reactancevalues are a'p'plied at the open mouth in of the stub l-l inshunt withthe'imp'edance of the guide ll.

In Fig. 3 is-illustrated asecond'form of tunable stub which may, likethe first ror'm, be connected to a waveguide carrying microwaves aseither'a' V series arm as shown in Fig. 1 or a shunt-arm as be made atthe longitudinal ce'nteriline or ingeneral in a region of maximumelectric field and in a direction parallel to the lines of electricfield intensity, the effect will be most pronounced and will beunaccompanied by any appreciable loss of energy.

The ends of the inserted portion of he Tin-are tapered to preventimpedance discontinuities and accompanying loss of energy. Theleng'th'ol the fin is made of the order of six or seven wavelengths and'its maximum depth of insertionis limited only by high voltage breakdownor shortcircuiting of the guide. Under these conditions a retardationofmicrowave energy of over 180 electrical degreesis easily attainable.

It is notable that the retardingactionof the fin on microwaves passingby itis doubly effective: microwaves-entering from the guide M areretarded as they passthe fin and after reflection fromthe closed'end I'2areretarded a. second. time as they return towardthe-guide t4.

y means of a fin such as described in a waveshown in Fig. 2. In Fig. 3the connection as a series arm is chosen for illustration. The stub 25is connected to the waveguide it through which microwaves aretransmitted. The end 3| .of' the stub 26 may be either closed oropensince in this form of the invention little of any microwave" energy willreach the end. The stub contains two longitudinal slots, one in thecenter line of each broad face, and each is protected by twocoamingsforming wave traps 32 and 3'3 such as described in the copendingapplication mentioned'supra. These wave traps produce high im- .pedanceat the slots for microwave energy attempting to escape therefrom.

.Afin 29 in the shape of a 'stri'pbf sheet material is hinged by a screw21 to two bosses'lii-ZB, more clearly shown in Fig. 4. The screwissupplied with a nut 31 so that when tightened it clampsthe bosses 28against the fin 29-andp'reve'nts'it from turning. By loosenin'g the nutthe finmay be moved into and clamped at a'ny'p'osi tion'suc'hia's theone shown in'Fig. 3 by full lines "orthat'shown by the 'dashedoutline34. In these two positions shown and at any intermediate position theedge 36 of the fin near the guide section 24 serves as ashort-circuiting post across the'guide, the effective position'of.theshort cir- 'cuit being near the'p'oint 38 where the finpasse's fineffect. This phase-retardation is accom-' plished without the productionof any impedance discontinuity because of the oblique position of theedge 36 in the guide.

The lines of intersection of the plane of the fin with the planes of thebroad faces of the guide are high impedance regions because of theaction of the trap coamings, so that microwave energy is prevented frompassing between the fin and the guide faces even when high potential ispresent.

Although rectangular hollow wave guide is used as an example in theembodiment of this invention, any other type of microwave guide can beemployed instead, for use with an adjustable fin, as is more fullyexplained in the copending application mentioned supra.

In Figs. 1 and 2 a screw is employed for adjusting the fin and in Fig. 3a clamping hinge is used. However any other convenient method foradjustment of the position of insertion of the fin maybe employedinstead.

What is claimed is:

1. A microwave tunable wave guide stub comprising, a rectangular waveguide section provided with longitudinal opposed openings in each of thebroad faces thereof, a fin of sheet metallic conductive material pivotedat one end to the external face of said wave guide section at a pointadjacent one end of one of said longitudinal openings, said finextending through said openings and across the narrow dimension of saidwave guide section, means for adjusting the angular position of said finabout said pivot, said fin being so shaped and the limits of angularadjustment being such that in any position of adjustment the area of thefin contained within the wave guide section increases gradually from oneend.

2. A microwave tunable wave guide stub comprising, a wave guide sectionprovided with longitudinal opposed openings in the periphery thereof, afin of sheet metallic conductive material pivoted at one end to theexternal face of said wave guide section at a point adjacent one end ofone of said longitudinal openings, said fin extending through saidopening and across said wave guide section, means for adjusting theangular position of said fin about said pivot, said fin being so shapedand the limits of angular adjustment being such that in any position ofadjustment the area of the fin contained within the Wave guide sectionincreases gradually from one end.

JOHN F. ZALESKI.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,427,098 Keizer Sept. 9, 19472,433,368 Johnson Dec. 30, 1947 2,457,695 Liskow Dec. 28, 1948 FOREIGNPATENTS Number Country Date 591,369 Great Britain Aug. 15, 1947 OTHERREFERENCES Microwave Transmission Circuits," edited by George F. Ragan,Radiation Laboratory Series, Vol. 9, first edition, published byMcGraw-Hill. copyright May 21, 1948.

